The aim of this proposal is to investigate the transcriptional and posttranslational regulation of the disease protein causing the polyglutamine (polygln) disease spinocerebellar ataxia type-3 (SCA3), a protein known as ataxin-3. Polygln diseases are dominantly inherited, ultimately fatal neurodegenerative diseases, for which there is no effective therapy. A unifying pathological feature of polygln diseases is intracellular aggregation of the disease protein, arguing that precise control of protein homeostasis is vital to neuronal survival. Therefore, therapeutic strategies should include efforts to: 1) enhance degradation of the disease protein; 2) boost the protein surveillance machinery of the neuron; and 3) modulate disease gene expression. Toward this goal, the specific aims are to determine the cellular pathways controlling ataxin-3 degradation, and to define the transcriptional regulation of the SCA3 disease gene, MJD1. Specifically, studies in aim 1 hope to demonstrate that ataxin-3 is a normal target for proteasome and caspase proteolysis, and determine whether the proteasomal activity is inhibited by accumulated, mutant polygln protein. Studies in aim 2 will test the hypothesis that the Ras/MEK pathway regulates MJD1 gene transcription. A variety of cellular and biochemical methods will be employed to answer these questions including metabolic pulse-chase assays, coimmunoprecipitation experiments, immunoblots, site-directed mutagenesis, cell synchronization, and promoter analysis. The studies proposed here will further our understanding of ataxin-3 production and degradation, perhaps leading to the development of therapies for these currently untreatable diseases.